In many abrading or polishing operations, a finer finish is desired on one part of a workpiece than on another part. A conventional method of producing such a final surface is to abrade the entire workpiece surface with a coarse abrasive, leaving a rough finish, after which a fine abrasive is used only on the part of the workpiece requiring the finer finish. An alternate method is to abrade the entire workpiece with a fine abrasive thus imparting a fine finish, and then roughening part of the surface with a coarse abrasive to provide the desired rougher section.
Personal computers, which have become common in the current times, frequently contain a rigid memory disk or hard drive, which involves a rigid thin film metal or nonmetal disk as the substrate for the magnetic medium coating. The annular surface of the thin film disk, which will be coated with magnetic media, requires a coarser finish on the inner portion of the annular surface and a finer finish on the outer portion of the annular surface. In one conventional arrangement, the thin film rigid disks are manufactured by electroless nickel plating a thin-film of nickel or nickel alloy onto an aluminum base, such as nickel/phosphorus (Ni--P), which is then polished to a very fine, mirror-like finish. After polishing, the Ni--P coating is textured, followed by the application of a magnetic coating(s) thereon to form the magnetic medium. Nonmetal substrates, such as glass or ceramic substrates, also are used in the rigid memory disk industry in place of the metal substrates. For these nonmetallic substrates, there is no metal or metal alloy coating applied onto the metal base before subsequent polishing, texturing, and magnetic coating application. Rather, the surface of the glass or ceramic rigid disk itself is polished, textured, and thereafter the magnetic coating is directly applied thereon without interposing any metal or metal alloy coating layer.
Rigid disks require a fairly consistent surface texture in order for the disk to perform properly. The texture provided on the surface of a thin film rigid disk is a compromise of the surface finish (Ra) necessary for the memory area versus the surface finish necessary for the head landing zone. The landing zone, typically a 1/8 inch to 3/8 inch (0.32 to 0.95 cm) wide inner annular portion of the disk, requires a relatively rough finish to minimize the stiction and friction between the disk and the read/write head on startup and shutdown of the drive. The texturing also eases the separation between the computer head and the rigid disk when the computer is first turned on. If the disk is smooth and untextured, it is difficult for the disk to start spinning because of too much head/disk contact. The surface roughness of the landing zone preferably has an Ra of about 40 to 60 Angstroms. In contrast, the memory retention area of the disk, typically the outer annular surface portion of the disk, does not need to be as rough, but is preferred to have an Ra of about 20 Angstroms. A lower Ra minimizes asperities on the disk surface and enables lower flying heights of the read/write head which results in higher recording densities.
The texturing process is critical to the performance of rigid disks. Texturing typically produces, on the annular surface of the disk which will bear the magnetic medium coating, a random pattern of uniform scratches with sharply defined edges in a substantially circumferential direction relative to the center of the rigid disk. Disk texturing accomplishes a number of purposes, including improving the aerodynamics between the computer head (which reads and writes data on the disk) and the surface of the magnetic coating on the disk. The scratches formed during texturing make it easier for the head to distinguish bytes of information between tracks on the disk. If the scratches are too deep, however, this may cause a loss of data on the rigid disk.
Disk surface texturing has traditionally been accomplished by using a loose abrasive slurry. Loose abrasive slurries provide the requisite substantially circumferential scratches that have sharply defined edges with the appropriate depth. The use of loose abrasive slurries is, however, accompanied by a number of disadvantages. For instance, the loose abrasive slurries create a large amount of debris and waste. As a result, the thin film rigid disks must be thoroughly cleaned to remove any residual surface residue from the abrasive slurry. The loose abrasive slurry also results in a relatively high amount of wear on the equipment used for texturing.
To overcome the above noted disadvantages associated with loose abrasive slurries, coated abrasive lapping films have been used to texture the thin film rigid disks. Such a lapping film typically comprises a polymeric film backing having an abrasive layer consisting of very fine abrasive particles dispersed in a binder. The abrasive layer is typically coated on the polymeric film to form a thin layer which has a surface profile which is essentially flat other than the partial protrusions of some of the abrasive particles. During use, the lapping film abrades a portion of the substrate surface to impart the texture therein. Recently the use of porous nonwoven cloths coated on a surface with an abrasive slurry has been advanced as an alternate to lapping film to uniformly texture thin film metal or metal alloy coated rigid disks before application of the magnetic coatings in a clean process that generates high quality scratches and avoids reweld, i.e., the reattachment of abraded metal particles on the surface being textured. For example, U.S. Pat. No. 5,307,593 (Lucker et al.) discloses a nonwoven substrate having an abrasive coating thereon that is used for texturing magnetic media substrates having a thin-film metal or metal alloy coating. The porous nonwoven substrate provides advantages such as the ability to collect and entrap swarf and debris during the abrasion. U.S. Ser. No. 08/301,254 (Wedell et al.) filed 6 Sep. 1994 and assigned to the assignee of the present invention, discloses combining the texturing characteristics of a loose abrasive slurry and a fixed abrasive tape by providing a water soluble abrasive coating on a nonwoven material.
Each of these methods, loose abrasive slurries, film backed lapping films, and nonwoven backed lapping products, requires, at a minimum, a second texturing step in order to produce the difference in surface texture needed on the disk between the memory area and the landing zone.
U.S. Pat. No. 875,936 (Landis) teaches an abrading material comprising a backing coated with relatively wide and narrow parallel abrasive coatings with adjacent strips each containing a different grade of two different abrasive grades and regions between the strips being devoid of any abrasive coating.
JP 4-141377 published 14 May 1992 teaches a roll of abrasive tape for flexible magnetic disks and magnetic tapes, where the abrasive grain size gradually increases from the free end of the tape to the center of the roll. The pressure of being wound counteracts the larger abrasive grain size and thus, when utilized, the abrasive tape has a uniform abrasiveness throughout the length of the tape as it is unwound from the roll.
JP 4-210383 published 31 Jul. 1992 teaches a roll of coated abrasive tape for the polishing of magnetic recording medium, where the hardness of the binder is varied along the length of the tape from the free end to the center of the roll. The pressure of being wound counteracts the binder hardness variance and thus, when utilized, the abrasive tape has a uniform abrasiveness throughout the length of the tape as it is unwound from the roll.
U.S. Pat. No. 5,166,006 (Lal et al.) teaches texturing thin film disks by use of a chemical etchant process.
U.S. Pat. No. 5,167,096 (Eltoukhy et al.) describes a disk-like abrasive pad having a backing comprising regions of different compressibilities which produce a deeper-groove texture opposite a less compressible part of the backing at the inner diameter of a disk.
U.S. Ser. No. 08/398,198 (Ohishi) filed 2 Mar. 1995 and assigned to the assignee of the current invention, teaches a method of texturing thin film rigid disks using an abrasive article comprising abrasive composites.
U.S. Ser. No. 08/514,417 (Stubbs et al.) filed 11 Aug. 1995 and assigned to the assignee of the current invention, teaches a method of making abrasive articles having at least two regions of abrasive coating abutting, wherein the regions having different abrasive natures, and method of making same.